Re: [PATCH v2 1/6] coresight: Add config flag to enable branch broadcast

[Mike Leach]

On Thu, 13 Jan 2022 at 09:11, James Clark <james.clark@xxxxxxx> wrote:
>
> When enabled, all taken branch addresses are output, even if the branch
> was because of a direct branch instruction. This enables reconstruction
> of the program flow without having access to the memory image of the
> code being executed.
>
> Use bit 8 for the config option which would be the correct bit for
> programming ETMv3. Although branch broadcast can't be enabled on ETMv3
> because it's not in the define ETM3X_SUPPORTED_OPTIONS, using the
> correct bit might help prevent future collisions or allow it to be
> enabled if needed.
>
> Signed-off-by: James Clark <james.clark@xxxxxxx>
> ---
>  drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
>  drivers/hwtracing/coresight/coresight-etm4x-core.c | 10 ++++++++++
>  include/linux/coresight-pmu.h                      |  2 ++
>  3 files changed, 14 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index c039b6ae206f..43bbd5dc3d3b 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -52,6 +52,7 @@ static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
>   * The PMU formats were orignally for ETMv3.5/PTM's ETMCR 'config';
>   * now take them as general formats and apply on all ETMs.
>   */
> +PMU_FORMAT_ATTR(branch_broadcast, "config:"__stringify(ETM_OPT_BRANCH_BROADCAST));
>  PMU_FORMAT_ATTR(cycacc,                "config:" __stringify(ETM_OPT_CYCACC));
>  /* contextid1 enables tracing CONTEXTIDR_EL1 for ETMv4 */
>  PMU_FORMAT_ATTR(contextid1,    "config:" __stringify(ETM_OPT_CTXTID));
> @@ -97,6 +98,7 @@ static struct attribute *etm_config_formats_attr[] = {
>         &format_attr_sinkid.attr,
>         &format_attr_preset.attr,
>         &format_attr_configid.attr,
> +       &format_attr_branch_broadcast.attr,
>         NULL,
>  };
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index bf18128cf5de..04669ecc0efa 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -692,6 +692,16 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>                 ret = cscfg_csdev_enable_active_config(csdev, cfg_hash, preset);
>         }
>
> +       /* branch broadcast - enable if selected and supported */
> +       if (attr->config & BIT(ETM_OPT_BRANCH_BROADCAST)) {
> +               if (!drvdata->trcbb) {
> +                       ret = -EINVAL;
> +                       goto out;
> +               } else {
> +                       config->cfg |= BIT(ETM4_CFG_BIT_BB);
> +               }
> +       }
> +
>  out:
>         return ret;
>  }
> diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
> index 4ac5c081af93..6c2fd6cc5a98 100644
> --- a/include/linux/coresight-pmu.h
> +++ b/include/linux/coresight-pmu.h
> @@ -18,6 +18,7 @@
>   * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
>   * directly use below macros as config bits.
>   */
> +#define ETM_OPT_BRANCH_BROADCAST 8
>  #define ETM_OPT_CYCACC         12
>  #define ETM_OPT_CTXTID         14
>  #define ETM_OPT_CTXTID2                15
> @@ -25,6 +26,7 @@
>  #define ETM_OPT_RETSTK         29
>
>  /* ETMv4 CONFIGR programming bits for the ETM OPTs */
> +#define ETM4_CFG_BIT_BB         3
>  #define ETM4_CFG_BIT_CYCACC    4
>  #define ETM4_CFG_BIT_CTXTID    6
>  #define ETM4_CFG_BIT_VMID      7
> --
> 2.28.0
>
Reviewed-by: Mike Leach <mike.leach@xxxxxxxxxx>

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK